Electrochromic devices, in which optical transmissivity is electrically controlled, are in current usage in building windows and in dimmable automotive rearview mirrors. Generally, electrochromic windows for a building are controlled with a driver and a user input, e.g., a dimmer control. Electrochromic rearview mirrors in automotive usage often have a light sensor aimed to detect light from headlights of automobiles, and are user-settable to engage an auto-dim function that adjusts the tint of the mirror based on input from the light sensor. There is a need in the art for a control system for electrochromic devices which goes beyond such basic settings and functions.